Work machines, for example, wheel loaders, track loaders, and the like, having work implements, such as buckets, are often used to dig material from one location, and dump the material at one or more other locations. For example, wheel loaders having buckets are used to dig materials such as gravel, sand, soil, and the like, and dump the material into the bed of a truck, or at other sites.
In a work environment in which the dig and dump process is performed repeatedly for long periods of time, it is desired to work as efficiently and productively as possible. However, as fatigue sets in, or if the operator is relatively inexperienced, the dig cycle may not be as productive as desired. This adversely impacts the efficiency of the work machine.
As a result, attempts have been made to automate the dig process to maximize productivity and efficiency. For example, it is known to automate the loading process of a work machine, such as a wheel loader, by monitoring various crowd factors as the bucket of the machine enters a pile of material. During the initial phase of the process, known systems determine that the bucket has entered the pile, and responsively begin to lift the bucket rapidly. The systems then tilt the bucket back as it continues to be lifted in a controlled manner.
The known systems are designed to operate with the engine of the work machine at full speed. However, there are situations where it is desired to push into a pile of material with the engine at a speed less than full throttle. For example, the ground may be wet or sandy, and thus not able to provide good traction. Maintaining the engine at full speed may then cause the work machine to slip excessively as it enters the pile. When the engine is operated at less than full speed, however, the known systems continue to command the same lift velocity as if at full speed. This may result in the bucket rising out of the pile without the automated dig cycle loading the bucket to capacity.
One improvement on the known systems is disclosed in commonly-owned U.S. Pat. No. 6,321,153 to Rocke et al. (the '153 patent). The '153 patent discloses a method which automates the loading process of a work machine by determining an actual engine speed relative to a full engine speed, and generating a lift velocity command that is based on a comparison of the actual engine speed to full engine speed.
However, the known systems, including the system of the '153 patent, do not account for the engine speed at less than the full engine speed or the ground speed at less than the maximum ground speed for a given gear. Furthermore, the known systems do not address the situation that arises when an operator downshifts when entering a pile, which may change engine speed, and consequently change the lift command.
Moreover, existing systems, including the system of the '153 patent, operate as though the bucket were always in the pile, once the systems are activated. Accordingly, if the system is activated by a small pile placed in front of a second larger pile, the bucket may rise so high before engaging the second pile that it does not capture a full load from the second pile.
The present invention is directed to overcoming one or more of the disadvantages set forth above or other disadvantages in the prior art.